FIG. 1 is a schematic drawing of one example of a conventional vacuum dryer including an upper chamber 21 and a lower chamber 31 made to communicate with each other. A thermal cycle is formed through the upper chamber 21 and lower chamber 31 using a compressor 24, a condenser 25, an expansion valve 26 and an evaporator 27. A vacuum pump 22 is connected to one side of the upper chamber 21 through a discharge pipe 23.
The evaporator 27 is positioned within the upper chamber 21, while the condenser 25 is positioned within the lower chamber 31. The compressor 24 and the expansion valve 26 are located outside of the two chambers 21 and 31.
With such a construction, an object to be dried is introduced into the lower chamber 31 through an opening therein (not shown) and power is turned on. The thermal cycle begins as the vacuum pump 22 is activated. Once the vacuum pump 22 as connected to the discharge pipe 23 has been activated, air is discharged from inside of the combination of the upper chamber 21 and lower chamber 31 through the discharge pipe 23. A vacuum is maintained in the upper chamber 21 and the lower chamber 31 during the drying process. In this condition, the compressor 24 within the thermal cycle continuously circulates a refrigerant or other comparable fluid through the system including the condenser 25, the expansion valve 26 and the evaporator 27.
When the thermal cycle is created, the condenser 25 discharges heat into the lower chamber 31, and the evaporator 27 absorbs heat from the upper chamber 21. Accordingly, due to the heat exchange within the two chambers, the temperature within the lower chamber 21 can be maintained within a range of about 40.degree. C. to 50.degree. C., and the temperature within the upper chamber 21 can be maintained at approximately 5.degree. C. Therefore, moisture can be evaporated from objects disposed in the lower chamber 31, condensed in the upper chamber 21, and discharged to outside the dryer by the vacuum pump 22.
Conventional vacuum dryers, as described above, have certain disadvantages. First, the conventional vacuum dryer has a complicated construction. Second, it is expensive to operate due to the cost of creating the thermal cycle for heat exchange in the chambers and the cost of transporting the dried material from the lower chamber because the volume of the dried material cannot be reduced significantly.